Proposed is the combining of tumor-targeted, biocompatible, contrast enabling nanoparticles with photoacoustic imaging (PAI). PAI is an emerging, simple, low cost, non-ionizing and non-invasive method. The aim of this combination is to achieve simultaneous structural and chemical/functional imaging. Recently, the emerging PAI technique has drawn considerable attention and has been explored for its potential application to a variety of diseases, including breast cancer, prostate cancer, melanoma and inflammatory arthritis. The proposed nanosonophore-based PAI method enables safe imaging, using only light and ultrasound, together with biocompatible, hydrogel-based, biodegradable and bio-eliminable nanoparticle contrast agents and sensors. The resultant non-invasive and non-ionizing PAI will enable morphological and functional evaluation, across the tumor, with both high spatial and high temporal resolution, but without any damage to the tissues. Currently no gold standard exists for such functional imaging. The proposed imaging method can be used for early detection and diagnosis of tumors, and for monitoring the progression of disease and of therapy. It could also observe phenomena at the molecular level in vivo and allow a better understanding of the pathophysiology of diseases as well as of disease onset, progression, and response to therapy. Using a nanoparticle contrast agent that enables multiple chemical and structural imaging functions, simultaneously, will free healthcare practitioners from having to perform a series of examinations with a diverse set of contrast agents so as to generate a complete diagnostic assessment. The Specific Aims are: 1. Optimization of Targeted Multi-functional Sonophoric Nanoparticles (NPs) as Contrast Agents for in-vivo Structural and Functional Photoacoustic Imaging. 2. Structural Imaging using Nanoparticles Targeted at the Tumor 3. Functional Imaging of the In-Vivo Distribution of Oxygen and pH Across Tumors. 4. Monitoring Tumor Therapy by a Combination of Structural and Functional Imaging.